Polyetherimide resins such as those described in U.S. Pat. No. 3,847,867 have become increasingly important. These resins may be produced in known manner by reaction between aromatic bis(ether anhydrides) and organic diamines. They, and various derivatives, possess highly desirable physical and electrical properties.
One of the most important classes of derivatives involves resins produced in part from polyisocyanate compounds. In these resins, the polyisocyanate compounds may be employed in forming either or both of the polymer backbone and side chains. Most commonly, they represent a cross-linking agent for the resins.
In U.S. Pat. No. 3,541,038, for example, high molecular weight polyimidamide resins are produced by condensation of tribasic acid anhydride with diisocyanate compounds. The resultant resins are especially useful for coil-impregnation or electrical insulation. Tough films can also be produced from solutions of them.
Such polyisocyanate compounds, preferably employed in blocked form, are also described in U.S. patent application Ser. No. 53,317, filed June 29, 1979, where they are reacted to cross-link various polyetherimides. The resultant products have a variety of specialized uses in, for example, enamels for electrical insulation, laminate binders and high temperature paints. Many general and additional uses are also known or apparent.
While the foregoing resins are satisfactory for many uses, further improvements are desired. Better performance, new uses and additional application or production techniques would enable substantial advancement in their pertinent art or arts.